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Relationship between Resolution Bandwidth and Recived signal - RF Cafe Forums

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venkataravi

Post subject: Relationship between Resolution Bandwidth and Recived signal Posted: Mon Sep 25, 2006 4:04 am

Captain

Joined: Thu Jul 27, 2006 7:36 am

Posts: 11

Location: Bangalore --India

Hi,

What is the relationship between Resolution Bandwidth and Received signal strength.

With Regards

Y.V.Ravi

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IR

Post subject: Posted: Mon Sep 25, 2006 1:25 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

There is no relationship as the RSSI deals with amplitude and the Resolution BW deals with frequency

_________________

Best regards,

- IR

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frmunder

Post subject: Posted: Mon Sep 25, 2006 6:10 pm

Lieutenant

Joined: Mon Sep 25, 2006 5:52 pm

Posts: 2

As IR stated, there is not a direct relationship; but having a large resolution bandwidth can make the noise power swamp a low level signal.

Noise power in a 1hz bandwidth is -174dBm. Increase your bandwidth, and your noise grows by 10*log(RBW).

So if your resolution bandwidth is 10MHz, your noise power is

-174dBm+10*log(10,000,000)=-107dBm.

If your signal is smaller than this level, it will be unrecognizable.

(For different modulation formats, you also need to add more power to demodulate, i.e. C/N)

To be able to "see" this signal, you must decrease your bandwidth (as long as your signal can be processed in the decreased bandwidth).

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IR

Post subject: Posted: Tue Sep 26, 2006 4:14 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

That is true, but if you want to see the whole picture then you shouldn't forget the tempearture contribution to the noise power:

Pn=KTB

Where:

K - Boltzmann's contasnt 1.38*10e-23 J/Kelvin

T - Relative temperature in Kelvin

B - The bandwidth

In logarithmic terms, this formula becomes:

Pn=-174dBm+10 log (T/To) + 10 log BW

So any temperature above To (290 Kelvin degrees=17 deg C) will also increase the noise power, and according to the explanation given above will limit the strength of the received signal.

So in conclusion RSSI is not related just to the BW, but also to surrounding temperature...

_________________

Best regards,

- IR

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